1. Field of the Invention
The present invention concerns an improvement in systems for recycling exhaust gases for antipollution purposes in internal combustion engines.
2. Description of the Prior Art
More and more severe restrictions on the emission of oxides of nitrogen in exhaust gases have led to general use of exhaust-gas recycling systems permitting attainment of high degrees of recycling over a wide range of operation.
In this connection, it is necessary in practice to adopt the degree of recycling of gases to the assimilation capacity of the motor to obtain the greatest reduction in oxides of nitrogen without adversely affecting motor operation prohibitively.
In most known systems the arrangement for control of recycling does not permit full exploitation of the possibilities of this method of treatment. The effectiveness of such systems is limited by the deterioration in motor operation at low loads and by the resultant increase in hydrocarbon emissions.
Actually, most often, the degree of recycling not only is not constant as a function of load, but even varies inversely with it, the opening of the regulating supply valve is controlled, in the most improved systems, by the motor air supply due to a pneumatic or mechanical linkage, but the recycled supply is likewise a function of the difference in pressure between the motor exhaust and intake, and thus of its loading.
In certain systems a correction is made in the opening of the valve or the difference in pressure upstream and downstream of the valve as a function of motor load, but they are complicated and do not appear to be commercially useful.